Tone quality control circuit for electrical musical instruments



Dec. 11, 1951 1, M HANERT 2,577,752

TONE: QUALITY CCNTRCL CIRCUIT FCR ELECTRICAL MUSICAL INSTRUMENTS Filed Aug. 22, 1949 o. ,MPLIFIEFZS VOLUME CONTROL X N mi@ O OIIIOIIIOOOOO I In Venter John M, Han ert Atty.

Patented Dec. l1, 1951 TONE QUALITY CONTROL CIRCUIT FOR ELECTRICAL MUSICAL INSTRUMENTS John M. Hanert, Park Ridge, Ill., assigner to Hammond Instrument Company, Chicago, Ill., a corporation of Delaware Application August 22, 1949, Serial No. 111,741

1 Claim. l

My invention relates generally to electrical musical instrufnents, and more particularly to improvements in the tone quality control apparatus and circuits for instruments of the electric organ type employing generators of substantially sine wave output as the tone signal sources.

In electric organs of the type shown in the patent granted to Laurens Hammond, No. 1,955,- 350 on April 24, 1934, low impedance electromagnetic generators are coupled to the output system through a low input impedance transformer hav- .ing a number of taps on its primary winding, and the generators are selectively connected to these taps through high impedance circuits. This type of tone control and output circuit has proved satisfactory in use, but the transformer1 was oostly due to the necessity of providing the accurately located taps on the primary winding. It is therefore a primary object of the invention to provide an improved tone quality control circuit for coupling the generators to the output system, using a conventional coupling transformer not having taps on its primary winding.

A further object is to provide an improved tone duality control circuit for electrical musical instruments by which the cost of production may be substantially reduced.

Other objects will appear from the following description, reference being had to the accompanying drawing, which is a schematic wiring diagram of the improved. tone quality control and output circuit.

The invention is illustrated in the drawing as applied to the output of four low impedance generators 2d, which are intended to be representative or the seventy four or more tone signal generators employed in the organ to provide substantially sine wave signals used for the production of the fundamental and harmonics of the tones controlled by the manuals. The generators 2t! may be of the rotary electromagnetic type shown in the Hammond patent, or may be of any other type capable of supplying the desired output, such as electronic oscillators, or vibratory reeds or the lil-:e provided with suitable pickups. Each of the generators 2Q has one terminal grounded and its other terminal connected through parallel resistances 22 to switch arms 2li operable by playing keys 2t of the manuals.

Depression of one of the keys causes the switch arms 2@ associated therewith to make contact with bus bars 3! to 3l respectively. The connections between the generators 2t :and the switch arms 2i are such that each of the bus bars receives the frequencies corresponding to a par- (Cl. SI1-1.21)

2 ticular harmonic partial of the operated keys. For example, the bus bar 3l may collect the frequencies for the fundamental, while the bus bars 32 to 3i respectively collect the frequencies for the 2d, 3rd, 4th, 5th, 6th and 8th harmonics.

Since the quality of a musical tone is deterii ed by the relative intensities of its partials, means are provided to enable the player to predetermine, at will, the relative amplitudes at which the partial tone signals are supplied to the output system of the instrument. This means comprises a coupling transformer All having a primary winding il and a secondary winding 42, the latter being connected to the output system which may comprise a volume or expression control and amplifier t4 supplying a speaker A resistance element 48 is connected across the primary winding 4| and has terminals and taps Ei to t. The resistance element 4B is of low value with respect to the values of resistanoes 22. For example, assuming that resistors 22 have relatively high values, in excess of 16 ohms, the total resistance of element 4B is preferably approximately one-half ohm. The taps l to 'l are so located that the resistance between the taps and the grounded terminal 0 increases logarithmically, the gradation being such that the intensity of the sound produced by the speaker will increase by apparently equal increments as a constant amplitude signal is impressed across the terminals 0 and I to 8 in succession. For eX- ample, resistances between taps I to S and ground of .014, .034, .062, .102, .158, .238, .351, and .511 ohms, respectively, have been found to be satisfactory.

The bus bars El to 3l are adapted to be connected to the terminals Q to B in any selected, or preselected, arrangements or combinations, to produce different tone qualities. These connecting means are herein shown in the simplest form, consisting merely of conductors 5t each having one end connected to one of the bus bars 3! to Si and its other end adapted to be connected to any one of the terminals to 8.

Whenever a partial is not present in the desired tone quality the bus bar BI-Bl corresponding to such partial should be connected to the grounded terminal by its conductor 5B to prevent signals impressed upon such bus bar from reaching the output system through suprious conducting paths which may be present when a number of playing keys are depressed at the same time.

Because the resistance 4B is of such low value, it may be made in the form of a tapering width strip of high resistance thin sheet metal soldered at intervals to the terminals 0 8. These terminals may be in the form of spaced conductor bars, insulated from one another, and the means for connecting the bus bars 3I-31 to these conductor bars may include pre-set key operated switches, and draw bars making contact with these conductor bars, as shown in said Hammond patent.

Thus, the use of a simple resistance element 48, of negligible cost, makes it possible to use a conventional transformer 4) of substantially reduced cost as compared with the cost of a transformer with a multi-tapped primary winding as used in the past.

While I have shown and described a particular embodiment of my invention, it will be apparent to those skilled in the art that numerous modifications and variations may be made in the form and construction thereof, without departing from the more fundamental principles of the invention. I therefore desire, by the following claim, to include within the scope of my invention all such similar and modified forms of the apparatus disclosed, by which substantially the results of the invention may be obtained by substantially the same or equivalent means.

I claim:

In a tone quality control apparatus for an electrical musical instrument having an output system and being of the type in which electrical tone frequency signals of substantially equally eiective amplitudes are impressed upon bus bars through decoupling resistances by the operation of playing keys, a multi-tapped resistance element of overall resistance small relative the values of the decoupling resistances and having terminals for connection to the output system, and means for selectively connecting the bus bars to the taps on the resistance element.

JOHN M. HANERT.

REFERENCES CTED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,956,350 Hammond M Apr. 24, 1934 2,283,432 George June 4, 1940 2,229,755 Manatt Jan. 28, 1941 

